A type of magnet material such as Nd2Fe14B, αFe/Nd2Fe14B, and Fe3B/Nd2Fe14B obtained by a melt span is limited to a thin band such as a ribbon or flake-shaped powder obtained by milling the same. For this reason, in order to obtain a bulk-shaped permanent magnet which is used in general, a technique is necessary which changes a type of material, that is, fixes the ribbon or the powder to a predetermined bulk in a certain manner. A basic powder fixing means in powder metallurgy is pressureless sintering, but since the ribbon needs to maintain a magnetic characteristic based on a metastable state, it is difficult to apply the pressureless sintering thereto. For this reason, a predetermined-shape bulk fixation is carried out just by using a coupling agent such as epoxy resin. For example, R. W. Lee, etc. have disclosed that a ribbon of (BH)max of 111 kJ/m3 is fixed by resin to thereby obtain an isotropic Nd2Fe14B-based bond magnet of (BH)max of 72 kJ/m3 [R. W. Lee, E. G. Brewer, N. A. Schaffel, “Hot-pressed Neodymium-Iron-Boron magnets” IEEE Trans. Magn., Vol. 21, 1958 (1985)] (see Non-patent Document 1).
In 1986, the present inventors have proved that a small-diameter annular isotropic Nd2Fe14B bond magnet of (BH)max of ˜72 kJ/m3, in which the Nd2Fe14B magnet powder obtained by milling the melt spun ribbon is fixed by epoxy resin, is suitable for a small-size motor in Japanese Patent Application No. S61-38830. Later, T. Shimoda has compared a characteristic of a small-size motor of the small-diameter annular isotropic Nd2Fe14B-based bond magnet with a characteristic of a small-size motor of Sm—Co-based radial anisotropic bond magnet, and has mentioned that the former is suitable [T. Shimoda, “Compression molding magnet made from rapid-quenched powder”, “PERMANENT MAGNETS 1988 UPDATE”, Wheeler Associate INC (1988)] (see Non-patent Document 2). The reports that the former is suitable for a small-size motor have been made by W. Baran [“Case histories of NdFeB in the European community”, The European Business and Technical Outlook for NdFeB Magnets, Nov. (1989)], G. X. Huang, W. M. Gao, S. F. Yu [“Application of melt-spun Nd—Fe—B bonded magnet to the micro-motor”, Proc. of the 11th International Rare-Earth Magnets and Their Applications, Pittsburgh, USA, pp. 583-595 (1990)], Kasai [“MQ1, 2&3 magnets applied to motors and actuators”, Polymer Bonded Magnets' 92, Embassy Suite O'Hare-Rosemont, Ill., USA, (1992)], etc., and the former has been widely used as an annular magnet for a permanent magnet motor of a telecommunication equipment, OA, AV, PC, and their peripheral equipments since 1990 (see Non-patent Documents 3, 4, and 5).
On the other hand, a study about magnet material in terms of melt spinning has been actively carried out since 1980. By using a material of which various alloy compositions are controlled in terms of a microstructure, such as nano composite material using an exchange coupling based on a microstructure of Nd2Fe14B-based, Sm2Fe17N3-based, or αFe, Fe3B-based, etc. with them, isotropic magnet powder having a different powder shape obtained in terms of a rapid solidification method other than a melt spinning can be used for an industrial purpose [for example, YASUHIKO IRIYAMA, “Development Tendency of High-performance Rare-earth BondMagnet”, Ministry of Education, Culture, Sports, Science and Technology, Innovation Creation Project/Symposium of Efficient Usage of Rare-earth Resource and AdvancedMaterial, Tokyo, pp. 19-26 (2002), B. H. Rabin, B. M. Ma, “Recent developments in Nd—Fe—B powder”, 120th Topical Symposium of the Magnetic Society of Japan, pp. 23-28 (2001), B M. Ma, “Recent powder development at magnequench”, Polymer Bonded Magnets 2002, Chicago (2002), S. Hirasawa, H. Kanekiyo, T. Miyoshi, K. Murakami, Y. Shigemoto, T. Nishiuchi, “Structure and magnetic properties of Nd2Fe14B/FexB-type nano composite permanent magnets prepared by strip casting”, 9th Joint MMM/INTERMAG, CA (2004) FG-05] (see Non-patent Documents 6, 7, 8, and 9).
Davies, etc. have reported that isotropic (BH)max is 220 kJ/m3 [H. A. Davies, J. I. Betancourt, C. L. Harland, “Nanophase Pr and Nd/Pr based rare-earth-iron-boron alloys”, Proc. of 16th Int. Workshop on Rare-Earth Magnets and Their Applications, Sendai, pp. 485-495 (2000)] (see Non-patent Document 10). However, it is supposed that of (BH)max of rapid solidified powder used for an industrial purpose is 134 kJ/m3 and (BH)max of isotropic Nd2Fe14B bond magnet is almost 80 kJ/m3.
Irrespective of the above description, the permanent magnet motor corresponding to an object of the invention has been continuously demanded to be more decreased in size, to be more increased in output, and to be more tranquil in accordance with an increase in performance of electric and electronic devices. Accordingly, it is obvious that the improvement of the representative magnetic characteristic of (BH)max of the magnet powder of the isotropic bond magnet is useful for an increase in performance of the corresponding motor. Accordingly, in a field of such isotropic bond magnet motor, the necessity of the anisotropic bond magnet motor increases [FUMITOSI YAMASITA, “Application and Anticipation of Rare-earth Magnet to Electronic Device”, Ministry of Education, Culture, Sports, Science and Technology, Innovation Creation Project/Symposium of Efficient Usage of Rare-earth Resource and Advanced Material, Tokyo, (2002)] (see Non-patent Document 11).
Incidentally, the Sm—Co-based magnet powder using the anisotropic magnet can obtain a high coercive force HCJ even when an ingot is milled. However, Sm or Co has a large problem of a resource balance, and thus is not widely used as an industrial material. On the contrary, Nd or Fe is advantageous in a view point of a resource balance. However, even when an ingot of Nd2Fe14B-based alloy or a sintered magnet is milled, the HCJ is small.
For this reason, regarding a manufacture of anisotropic Nd2Fe14B magnet powder, a study that melt spinning material is used as an initial material has been carried out in advance.
In 1989, TOKUNAGAhas obtained the anisotropic bond magnet of (BH)max of 127 kJ/m3 in such a manner that a bulk in which Nd14Fe80-xB6Gax (X=0.4 to 0.5) subjected to a hot upsetting (Die-upset) is milled to obtain anisotropic Nd2Fe14B powder of HCJ=1.52 MA/m and hardened by resin [GARYO TOKUNAGA, “Magnetic Characteristic of Rare-earth Bond Magnet”, Fine Particle and Powder metallurgy, Vol. 35, pp. 3-7, (1988)] (see Non-patent Document 12).
In 1991, H. Sakamoto, etc. have manufactured anisotropic Nd2Fe14B powder of HCJ of 1.30 MA/m by subjecting Nd14Fe79.8B5.2Cu1 to a hot rolling [H. Sakamoto, M. Fujikura and T. Mukai, “Fully-dense Nd—Fe—B magnets prepared from hot-rolled anisotropic powders”, Proc. 11th Int. Workshop on Rare-earth Magnets and Their Applications, Pittsburg, pp. 72-84 (1990)] (see Non-patent Document 13).
As described above, there is known powder in which Ga or Cu is added to improve a hot rolling performance and a crystalline diameter of Nd2Fe14B is controlled to obtain a high HCJ. In 1991, V. Panchanathan, etc. have manufactured anisotropic bond magnet of (BH)max of 150 kJ/m3 in such a manner that hydrogen enters from a grain boundary in terms of a milling method of a hot rolling bulk to thereby break down into Nd2Fe14BHx and HD (Hydrogen Decrepitation)-Nd2Fe14B particle is dehydrogenated in terms of a vacuum heating [M. Doser, V. Panchanacthan, and R. K. Mishra, “Pulverizing anisotropic rapidly solidified Nd—Fe—B materials for bonded magnets”, J. Appl. Phys., Vol. 70, pp. 6603-6805 (1991)] (see Non-patent Document 14).
In 2001, Iriyama has improved anisotropic bond magnet of (BH)max of 177 kJ/m3 in such a manner that Nd0.137Fe0.735Co0.067B0.055Ga0.006 is formed into a particle of 310 kJ/m3 in the same way [T. Iriyama, “Anisotropic bonded NdFeB magnets made from hot-upset powders”, Polymer Bonded Magnet 2002, Chicago (2002)] (see Non-patent Document 15).
Meanwhile, Takeshita, etc. have suggested an HDDR method in which Hydrogenation (Hydrogenation, Nd2[Fe, Co]14 BHx) of Nd2(Fe, Co)14B phase occurs and, Decomposition (Decomposition, NdH2+Fe+ Fe2B), Desorpsion (Desorpsion), and Recombination (Recombination) occur at 650 to 1,000° C. [T. Takeshita, and R. Nakayama, “Magnetic properties and micro-structure of the Nd—Fe—B magnet powders produced by hydrogen treatment”, Proc. 10th Int. Workshop on Rare-earth Magnets and Their Applications, Kyoto, pp. 551-562 (1989)], and in 1999, have manufactured anisotropic bond magnet of (BH)max of 193 kJ/m3 from HDDR-Nd2Fe14B particle [K. Morimoto, R. Nakayama, K. Mori, K. Igarashi, Y. Ishii, M. Itakura, N. Kuwano, K. Oki, “Nd2Fe14B-based magnetic powder with high remanence produced by modified HDDR process”, IEEE. Trans. Magn., Vol. 35, pp. 3253-3255 (1999)] (see Non-patent Documents 16 and 17).
In 2001, Mishima, etc. have reported d-HDDR Nd2Fe14B particle of Co-free [C. Mishima, N. Hamada, H. Mitarai, and Y. Honkura, “Development of a Co-free NdFeB anisotropic magnet produced d-HDDR processes powder”, IEEE. Trans. Magn., Vol. 37, pp. 2467-2470 (2001)], and N. Hamada, etc. have manufactured a cubic anisotropic bond magnet (7 mm×7 mm×7 mm) of (BH)max of 213 kJ/m3 and a density of 6.51 Mg/m3 in such a manner that the d-HDDR anisotropic Nd2Fe14B particle is compressed by 0.9 GPa at 150° C. in the presence of an oriented magnetic field of 2.5 T [N. Hamada, C. Mishima, H. Mitarai and Y. Honkura, “Development of anisotropic bonded magnet with 27 MGOe”, IEEE. Trans. Magn., Vol. 39, pp. 2953-2956 (2003)] (see Non-patent Documents 18 and 19). However, the cubic magnet is not suitable for a general permanent magnet motor.
Meanwhile, in 2001, there is reported an injection forming bond magnet of (BH)max of ˜119 kJ/m3 using RD (Reduction & Diffusion)-Sm2Fe17N3 fine powder [JUN KAWAMOTO, KAYO SIRAISI, KAZUTOSI ISIZAKA, SINNICHI YASUDA, “15 MGOe-grade SmFeN Injection Forming Compound”, Magnetics Seminar of Electric Association, (2001) MAG-01-173] (see Non-patent Document 20). In 2002, Ohmori has reported an anisotropic magnet manufactured by an injection forming of (BH)max of 136 kJ/m3 using weather-resistant RD-Sm2Fe17N3 fine powder of (BH)max of 323 kJ/m3 [K. Ohmori, “New era of anisotropic bonded SmFeN magnets”, Polymer Bonded Magnet 2002, Chicago (2002)] (see Non-patent Document 21). There is reported that an increase in output of a ferrite sintered magnet is realized by using a surface magnet (SPM) rotor applied with an anisotropic Sm2Fe17N3 bond magnet of (BH)max of 80 kJ/m3 in terms of such an injection forming radial anisotropic [ATSUSI MATSUOKA, TOUGO YAMAZAKI, HITOSI KAWAGUCHI, “Investigation of Increase in Performance of Blowing Brushless DC Motor”, Rotating Equipment Seminar of Electric Association, (2001) RM-01-161] (see Non-Patent Document 22).
However, in the radial oriented magnetic field, when a forming ring cavity decreases in diameter (or increases in length), since most of a magnetomotive force is consumed as a leakage magnetic flux, the oriented magnetic field reduces. Accordingly, (BH)max reduces in a radial direction in accordance with a reduction of an orientation degree and in accordance with a decrease in diameter (an increase in length) irrespective of a bond magnet or a sintered magnet [for example, MOTOHARU SIMIZU, NOBUYUKI HIRAI, “Nd—Fe—B-based sinter-type anisotropic ring magnet”, Hitachi Metals Technical Review, Vol. 6, pp. 33-36 (1990)] (see Non-patent Document 23). Since it is difficult to generate a homogeneous radial magnetic field, a problem arises in that productivity is lower than that of the isotropic bond magnet.
However, when the magnetic characteristic in a radial direction is not dependent on a shape, a homogenous orientation is possible, and high productivity can be realized, it is possible to expect a distribution of a high (BH)max radial anisotropic magnet suitable for an increase in performance of the permanent magnet motor.
Therefore, the present inventors have disclosed a magnet manufacturing technique and its magnetic characteristic in which a compound of a coupling agent and magnet powder is compressed, and a cross-linking macromolecule of the coupling agent formed after a self-organization is mechanically stretched so that an anisotropic direction is changed to a radial direction in terms of a sintering deformation of the stretched perpendicular anisotropic thin-film magnet [F. Yamashita, S. Tsutsumi, H. Fukunaga, “Radially Anisotropic Ring- or Arc-Shaped Rare-Earth Bonded Magnets Using Self-Organization Techniqu”, IEEE Trans. Magn., Vol. 40, No. 4 pp. 2059-2064 (2004)] (see Non-patent Document 24). Accordingly, it is possible to manufacture a radial anisotropic magnet having a thickness of 1 mm or so of which a magnetic characteristic hardly reduces even when realizing a decrease in diameter (or an increase in length).
Meanwhile, in an iron core of an iron core-equipped permanent magnet motor, there are a slot for mounting excitation winding wires and teeth for forming a part of a magnetic circuit together with a magnet. In such an iron core structure, when the motor rotates, a torque pulsation, that is, cogging torque is generated in accordance with a permeance variation between the iron core and the magnet. The cogging torque prevents smooth rotation of the motor to make the cause impairing tranquility or controllability of the motor. Such cogging torque is apparently generated in the high (BH)max radial anisotropic magnet for generating a strong static magnetic field with a rectangular wave shape. Accordingly, it may be understood that an increase of the cogging torque disturbs an application in which the high (BH)max radial anisotropic magnet is applied to the permanent magnet motor.
As a cogging torque reducing method, there are known a method in which a magnetic pole of an iron core or a magnet is skewed or a gap between the iron core and the magnet is set to an irregular distance, a polar anisotropy method in which a magnetization direction of the magnet is set to a magnetic flux flow, a halbach method, and the like. Particularly, the halbach method of fitting segment magnets is suitable for the reduction of the cogging torque [YOSIDA, KESAMARU, SANG, “Reduction of Cogging Torque and Rotor Iron Core in terms of Segment-type Magnetization Method of Surface PM Synchronization Motor”, IEEJ. Trans. IA, Vol. 124, pp. 114-115 (2004)] (see Non-patent Document 25).
However, when the magnetic pole is separated into segments, since assembling precision largely influences the cogging torque, and a limitation in an actual shape or a configuration and complexity are overlapped, its production is difficult.
For example, a perpendicular anisotropic thin-film magnet having a thickness of 0.97 mm and (BH)max=162 kJ/m3 including a self organized coupling agent is anisotropically stretched to be thereby formed into a circular arc shape having a radius of 3.55 mm, an outer radius of 3.65 mm, a maximum thickness of 0.88 mm, and a length of 10 mm. When the magnet is magnetized in a pulse magnetic field of 4 MA/m, a magnetic flux becomes 1.53 times larger than a magnetic flux amount of an isotropic Nd2Fe14B bond magnet of (BH)max of 72 kJ/m3, and thus start torque of an iron core-equipped permanent magnet motor increase 1.4 times or more [F. Yamashita, H. Fukunaga, “Radially-Anisotropic Rare-Earth Hybrid Magnet with Sel-Organizing Binder Consolidated Under a Heat and a Low-Pressure Configuration”, Proc. 18th Int. Workshop on High Performance Magnets and Their Applications, Annecy, France, pp. 76-83 (2004)].
However, when a thickness of the magnet is, for example, 1.5 mm, since it is difficult to anisotropically stretch the perpendicular anisotropic thin-film magnet, there is a limitation in the thickness of the magnet in a deformation in which the magnetic characteristic is maintained. In a structure in which electromagnetic winding wires are arranged on a surface of the iron core opposed to the magnet, the iron core is provided with teeth and slots. For this reason, the cogging torque increases due to a permeance variation in accordance with a rotation of the motor. Particularly, the radial anisotropic magnet having a gap magnetic flux density distribution of a rectangular wave shape and a strong static magnetic field has the cogging torque 15 times or more that of the isotropic Nd2Fe14B bond magnet.
As described above, as the cogging torque reducing means, many studies and ideas have been made. Particularly, the halbach method of fitting the segment magnets is suitable for the reduction of the cogging torque [YOSIDA, KESAMARU, SANG, “Reduction of Cogging Torque and Rotor Iron Core in terms of Segment-type Magnetization Method of Surface PM Synchronization Motor”, IEEJ. Trans. IA, Vol. 124, pp. 114-115 (2004)]. However, when the magnetic pole is separated into segments, assembling precision critically influences the cogging torque. The limitation in the actual shape or the configuration and complexity are overlapped, which is difficult to be carried out in an industrial field. For this reason, in the radial anisotropic magnet, a radial anisotropic magnet manufacturing method has been demanded which is capable of being used in a combination of a known technique such as uneven thickness or skew without separating the magnetic pole and of remarkably reducing cogging torque while maintaining an output characteristic.
Non-patent Document 1: R. W. Lee, E. G. Brewer, N. A. Schaffel, “Hot-pressed Neodymium-Iron-Boron magnets” IEEE Trans. Magn., Vol. 21, 1958 (1985)
Non-patent Document 2: T. Shimoda, “Compression molding magnet made from rapid-quenched powder”, “PERMANENT MAGNETS 1988 UPDATE”, Wheeler Associate INC (1988)
Non-patent Document 3: W. Baran, “Case histories of NdFeB in the European community”, The European Business and Technical Outlook for NdFeB Magnets, Nov. (1989)
Non-patent Document 4: G. X. Huang, W. M. Gao, S. F. Yu, “Application of melt-spun Nd—Fe—B bonded magnet to the micro-motor”, Proc. of the 11th International Rare-Earth Magnets and Their Applications, Pittsburgh, USA, pp. 583-595 (1990)
Non-patent Document 5: Kasai, “MQ1, 2 & 3 magnets applied to motors and actuators”, Polymer Bonded Magnets' 92, Embassy Suite O'Hare-Rosemont, Ill., USA, (1992)
Non-patent Document 6: YASUHIKO IRIYAMA, “Development Tendency of High-performance Rare-earth Bond Magnet”, Ministry of Education, Culture, Sports, Science and Technology, Innovation Creation Project/Symposium of Efficient Usage of Rare-earth Resource and Advanced Material, Tokyo, pp. 19-26 (2002)
Non-patent Document 7: B. H. Rabin, B. M. Ma, “Recent developments in Nd—Fe—B powder”, 120th Topical Symposium of the Magnetic Society of Japan, pp. 23-28 (2001)
Non-patent Document 8: B M. Ma, “Recent powder development at magnequench”, Polymer Bonded Magnets 2002, Chicago (2002)
Non-patent Document 9: S. Hirasawa, H. Kanekiyo, T. Miyoshi, K. Murakami, Y. Shigemoto, T. Nishiuchi, “Structure and magnetic properties of Nd2Fe14B/FexB-type nano composite permanent magnets prepared by strip casting”, 9th Joint MMM/INTERMAG, CA (2004) FG-05
Non-patent Document 10: H. A. Davies, J. I. Betancourt, C. L. Harland, “Nanophase Pr and Nd/Pr based rare-earth-iron-boron alloys”, Proc. Of 16th Int. Workshop on Rare-Earth Magnets and Their Applications, Sendai, pp. 485-495 (2000)
Non-patent Document 11: FUMITOSHI YAMASITA, “Application and Anticipation of Rare-earth Magnet to Electronic Device”, Ministry of Education, Culture, Sports, Science and Technology, Innovation Creation Project/Symposium of Efficient Usage of Rare-earth Resource and Advanced Material, Tokyo, (2002)
Non-patent Document 12: GARYO TOKUNAGA, “Magnetic Characteristic of Rare-earth Bond Magnet”, Fine Particle and Powder metallurgy, Vol. 35, pp. 3-7, (1988)
Non-patent Document 13: H. Sakamoto, M. Fujikura and T. Mukai, “Fully-dense Nd—Fe—B magnets prepared from hot-rolled anisotropic powders”, Proc. 11th Int. Workshop on Rare-earth Magnets and Their Applications, Pittsburg, pp. 72-84 (1990)
Non-patent Document 14: M. Doser, V. Panchanacthan, and R. K. Mishra, “Pulverizing anisotropic rapidly solidified Nd—Fe—B materials for bonded magnets”, J. Appl. Phys., Vol. 70, pp. 6603-6805 (1991)
Non-patent Document 15: T. Iriyama, “Anisotropic bonded NdFeB magnets made from hot-upset powders”, Polymer Bonded Magnet 2002, Chicago (2002)
Non-patent Document 16: T. Takeshita, and R. Nakayama, “Magnetic properties and micro-structure of the Nd—Fe—B magnet powders producedbyhydrogen treatment”, Proc. 10th Int. Workshop on Rare-earth Magnets and Their Applications, Kyoto, pp. 551-562 (1989)
Non-patent Document 17: K. Morimoto, R. Nakayama, K. Mori, K. Igarashi, Y. Ishii, M. Itakura, N. Kuwano, K. Oki, “Nd2Fe14B-based magnetic powder with high remanence produced by modified HDDR process”, IEEE. Trans. Magn., Vol. 35, pp. 3253-3255 (1999)
Non-patent Document 18: C. Mishima, N. Hamada, H. Mitarai, and Y. Honkura, “Development of a Co-free NdFeB anisotropic magnet produced d-HDDR processes powder”, IEEE. Trans. Magn., Vol. 37, pp. 2467-2470 (2001)
Non-patent Document 19: N. Hamada, C. Mishima, H. Mitarai and Y. Honkura, “Development of anisotropic bonded magnet with 27 MGOe”, IEEE. Trans. Magn., Vol. 39, pp. 2953-2956 (2003)
Non-patent Document 20: JUN KAWAMOTO, KAYO SIRAISI, KAZUTOSI ISIZAKA, SINNICHI YASUDA, “15 MGOe-grade SmFeN Injection Forming Compound”, Magnetics Seminar of Electric Association, (2001) MAG-01-173
Non-patent Document 21: K. Ohmori, “New era of anisotropic bonded SmFeN magnets”, Polymer Bonded Magnet 2002, Chicago (2002)
Non-patent Document 22: ATSUSIMATSUOKA, TOUGOYAMAZAKI, HITOSI KAWAGUCHI, “Investigation of Increase in Performance of Blowing Brushless DC Motor”, Rotating Equipment Seminar of Electric Association, (2001) RM-01-161
Non-patent Document 23: MOTOHARUSIMIZU, NOBUYUKI HIRAI, “Nd—Fe—B-based sinter-type anisotropic ring magnet”, Hitachi Metals Technical Review, Vol. 6, pp. 33-36 (1990)
Non-patent Document 24: F. Yamashita, S. Tsutsumi, H. Fukunaga, “Radially Anisotropic Ring- or Arc-Shaped Rare-Earth Bonded Magnets Using Self-Organization Technique”, IEEE Trans. Magn., Vol. 40, No. 4 pp. 2059-2064 (2004)
Non-patent Document 25: Yoshida, Kesamaru, Sano, “Reduction of Cogging Torque and Rotor Iron Core in terms of Segment-type Magnetization Method of Surface PM Synchronization Motor”, IEEJ. Trans. IA, Vol. 124, pp. 114-115 (2004)